The invention relates to an ultrasonic diagnosis system assembled into an endoscope, and more particularly, to such system which includes an ultrasonic wave transmitting and receiving transducer rockably mounted within the distal end of a portion of an endoscope which is adapted to be inserted into a coeliac cavity to effect a B-mode sector scan thereof to produce a reconstructed image of internal tissues.
As is recognized, the recent advance in the ultrasonic imaging art has established an ultrasonic diagnosis technique which is extensively useful for diagnostic purposes by forming an echo image by means of an ultrasonic scanning of an affected part of a physical body. The technique comprises transmitting an ultrasonic wave into the physical body of a patient from the surface thereof, receiving a reflected wave or echo from the interior, and forming an ultrasonic tomographic image of various organs within the body on the basis of acoustical information contained in the reflected wave, thus enabling the image to be utilized for purpose of diagnosis.
The described ultrasonic imaging technique has a number of advantages over the radiography which has been conventionally used in the medical art in that an image of soft tissues of a living body can be easily produced without the use of contrast medium, that the technique is free from the likelihood of causing adverse influences of radioactivity and is harmless to a living body, that it lends itself to locate calculus or cancer tissues, and that the equipment required is inexpensive and easy to operate. The technique has rapidly increasing applications inasmuch as the quality of the image formed is greatly improved as a result of the recent advance in the art.
However, with the conventional ultrasonic diagnosis system, in almost every instance, the ultrasonic wave is transmitted from and received on the surface of the physical body of a patient in order to produce an image of various organs located within the body. Hence, the distance to the organ being scanned is usually large enough to prevent a sharp image of high resolution from being produced. Moreover, the passage of the ultrasonic wave through a non-uniform layer such as subcutaneous fat results in a reduction in the S/N ratio of the echo signal. Alternatively, the presence of a gaseous layer such as a coeliac cavity or air-bladder in the path of the ultrasonic wave causes the ultrasonic energy to be absorbed and attenuated, even leading to a difficulty in the imaging process. In addition, when the organ is located behind a bone, the imaging is disabled by the attenuation of the ultrasonic wave which is either reflected or absorbed by the bone.
To overcome these drawbacks or difficulties experienced in the ultrasonic imaging process when the wave is transmitted from the surface of the physical body, it has been proposed to transmit an ultrasonic wave from within a coeliac cavity in producing an image of internal organs. As compared with ultrasonic imaging from the outer surface of the physical body, the ultrasonic imaging from within a coeliac cavity offers a number of major advantages:
(1) in that a diagnosis from a location more closely spaced from an organ of a living body is made possible, permitting the use of an ultrasonic wave of higher frequency with improved resolution;
(2) a diagnosis of those organs which have been heretofore difficult or impossible to image from the outer surface due to the presence of coeliac cavity, air-bladder or bone is made possible; and
(3) the process is not subject to the influence of subcutaneous fat which varies from patient to patient, enabling a more accurate diagnosis. Several types of apparatus have already been proposed which are directed to the ultrasonic imaging from within a coeliac cavity. By way of example, an ultrasonic diagnostic apparatus is known in which an ultrasonic transducer is placed into the rectum and rotated within a pouch containing water to effect a radar scan for examining the prostate gland. Also known is an arrangement including a transducer which is mounted in the distal end of a catheter for insertion into the main artery or the heart, or an arrangement including an ultrasonic transducer which is mounted on the tubular side of a sonde which is mounted for axial displacement for scanning purpose. Finally, an arrangement is also known in which a plurality of ultrasonic transducers are disposed in an array on the tubular side of a sonde along the axial direction or the circumferential direction and are electrically switched in a sequential manner to provide a linear scan.
However, these ultrasonic diagnosis systems are not provided with means which permits an optical observation of the interior of a coeliac cavity, so that when any one of these systems is inserted into the coeliac cavity, there remains a disadvantage that the location where the ultrasonic transducer is disposed within the cavity or in which direction it is oriented cannot be known. Also, when the system is being inserted into the coeliac cavity, the inability to observe the interior of the coeliac cavity creates a risk. While the placement of the system into a relatively shallow coeliac cavity having a simple configuration such as the rectum or the gullet may be possible, it is very difficult to place it into a coeliac cavity which is complex in configuration and has a substantial depth such as the stomach, the duodenum or the colon, requiring a very high level of skill. Hence, it is obvious that there is a need for an ultrasonic diagnosis system capable of an ultrasonic imaging and which permits an optical observation of the interior of a coeliac cavity.
On the other hand, an endoscope is popularly utilized to provide an optical observation of the interior of a coeliac cavity. Hence, it would appear that an ultrasonic diagnosis system which eliminates the described disadvantages can be obtained by assembling an ultrasonic transducer into the distal end of an endoscope which is provided with an optical observation unit which permits an observation of a coeliac cavity. However, the implementation of such an ultrasonic diagnosis system involves the following two technical problems:
(1) A medical endoscope which can be inserted into a coeliac cavity without undue pain or damage to a patient must be limited in its thickness. By way of example, the limit on the diameter of an endoscope which is passed through the gullet to observe the stomach or the duodenum is on the order of 13-14 mm. Accordingly, an ultrasonic transducer of a reduced size must be used in order to incorporate it into the endoscope. However, a currently available ultrasonic transducer assembly which is used to provide an electronic sector scan and including a plurality of elements has dimensions on the order of 10.times.13.times.16 mm, and hence cannot be received within the endoscope. Thus, only a single element, ultrasonic transducer can be used.
(2) When a single element, ultrasonic transducer is employed to produce a two-dimensional tomographic image, some mechanical scan technique must be used. To this end, a drive mechanism must be incorporated into the endoscope.
In consideration of these factors, it will be seen that a B-mode mechanical sector scan technique using a single element, ultrasonic transducer will be an optimum solution to the incorporation of an ultrasonic diagnosis system into an endoscope while overcoming the problems mentioned under (1) and (2) above. The B-mode mechanical sector scan technique permits an imaging over an extensive area of a living body with a limited rocking motion of the ultrasonic transducer, and thus is optimally adapted to be used in an arrangement such as an endoscope which affords a limited space.